Pulse communication system employing pulse frequency reduction for signaling



Apnl 6, 1948. E. M. DELORAINE ETAL 2,438,903

PULSE COMMUNICATION SYSTEM EMPLOYING PULSE FREQUENCY REDUCTION FORSIGNALING Filed oct. 11, 1945 `TIME A T OHNE Y Patented Apr. 6, 1948PULSE .COMVIUNICATION SYSTEM EMPLOY- ING PULSE FREQUENCY REDUCTION FORSIGNALING Edmond M. Deloraine, New York, and Donald D. Grieg, ForestHills, N. Y., assignors to Federal Telephone and .Radio Corporation, NewYork, N. Y., a corporation of Delaware Application October 11, 1943,`Serial No. 505,778

This invention relates to signaling systems and more particularly Vtosignaling systems adapted for use in regular intelligence communicationsystems.

In vthe normal telegraph and telephone ycommunication systemsusing-amplitude or frequency 6 Claims; (Cl. 179-15) modulation,particularly carrier communication A systems, the transmission ofringing and the like signaling has generally constituted a relativelycomplex problem. With the use of `modulated impulses for transmissionVof intelligence, simplied forms of signaling devices are readilypossible. Such arrangements are broadly disclosed in the copendingapplication of E. M. Deloraine, entitled Communication and signalingsystem, led on October 4, 1943, lSerial No. 504,881.

It is an object of our invention to provide a signaling system vof anovel character for use with modulated impulse communication systems.

It is a further object of our invention `to provide the signaling systemfor use in impulse modulation systems wherein the signal receptive meansmaybe connected directly to the output of the demodulating receiver.`

Other objects of our invention and specific features thereof will becomeapparent from a reading of the particular description of an embodimentthereof made with reference to the accompanying drawing, inwhich:

Fig. 1 is a block circuit diagram of a system embodying our invention;and

Fig. 2 is a setof curves used in explainingthe operation ofthe system ofFig. 1.

In Fig. 1, a multiplex impulse communication system is diagrammaticallyshown comprising a source of synchronizing Waves supplying VcontrolWaves to impulse modulator and through phase Shifters I4 and I5 tootherimpulse modulators I2 and I3. It `should beunderstood that while onlythree channels are'shown in the present system, other modulators may heprovided to furnish as many -channels as the line can properly carry.'The `outputs from impulse modulators |I, |2 and f|3 are applied to acommon line I8, preferably a coaxial line or other high frequencycarrier line.` -In 'place of a transe mission line, radio transmissionmay be `used if desired. These impulses because-of phase Shifters I4 andI5, are inter-leaved `one with the other to provide a resultant Wave of`impulses 2 and 3, as shown in curve a ofEig. 2.

These impulses areapplied `to a synchronizing control oscillator orother means of any suitable type 20 and to `channel selectors 2|, 22 and23. At the same time, 'synchronizing control output 2 is applied tochannel selector 2| and over phase shifters 24 and `25 to channelselectors 22` and 23, to select the desired channelbefore demodulatingthe received impulses in the normal manner. The selected impulses fromchannel selec,- tor 2| are applied over line 26 and condenser 21 to thevoice or other frequency reproducing demodulating apparatus 3|.Similarly, the output from each `channel selector 22 and 23 is appliedover lines 26A, 26B and condensers 21A,

21B, respectively, to other demodulators $32, 33.

The impulses I, 2 and 3 are modulated, preferably in time position, inaccordance with the sound signals to be transmitted. Thus, the soundsignals derived from the impulses are applied at the output ofdemodulators 3|, 32 and 33. It is clear that Vpulse amplitude modulationmay be used instead of time modulation, if desired, in which case theVdemodulators will serve to reproduce the sound frequency envelopedirectly. Thus, in normal operation, the separate channels are used forseparate communications.

-In accordance with our invention, when it is desired'to signal to aVreceiving station to indicate that intelligence signals are to betransmitted or for some other purpose, a frequency divider is provided4to reduce the number of `impulses in that; channel to a ringing orsignaling frequency. To this end, turning first to thechannelusingmodulator and channel selector 2|, We provide a frequencydivider I6 controlled by synchronizing source -|0. This frequencydivider comprises a square Wave generator VIta', and a mixer and clipperIb to provide a Wave of the form such as 30 shown in curve b which isadded to the impulse train serving to elevate every fourth impulse fromthe output koin-icdulator I These elevated impulses are then clipped atthe level indicated by clipping line 3|a so that only every fourthimpulse from modulator is applied to line I8.

It should be understood that the factor of frequency division is shownonly by Way of illustration. Normally, the number of impulses applied tothe line would be in the order of twelve thousand per second. It wouldusually be preferable then to reduc-e the frequency to some valuedepending on the ringing connection used. Where the output of thedemodulator is `used to supply theringing energy a value such as or 300pulses or cycles per second would he used, so that the frequencydivision normally would be much greater than-that shown in itssimplliedform for purposes of illustration.

and since these are at a low frequency level as indicated by theelevated impulses of curve c, the output of channel selector 2I willprovide this low signaling frequency as indicated by the impulses abovethe clipping level 33a of curve c. Condenser 21 preferably is selectedso that it does not pass this low frequency and all the low frequency istherefore shunted over low pass-filter 28 to signaling buzzer 29. Thus,the signaling unit may be connected directly across. line 2li..f

Instead of providing a separate low pass filter there are provided insaid train substantially only impulses recurring at a given low cadencefrequency, receiver 'means for receiving said .impulses, and signalmeans responsive to said impulses of said low cadence frequency coupleddirectly to said receiver means for producing said signals, said meansfor effectively selecting said impulses comprising a frequency dividerinclud- Ving a square wave generator, a mixer and a clipper, meanscoupling the output of said generator to saidmiXer and clipper, andmeans for selectively inserting and removing said frequency divider fromthe circuit.

. ,-2. A transmission system comprising a source of impulses forproducing impulses having a normal spacing providing a cadence frequencyfor saidimpulses higher than the frequency of in- 28, buzzer 29 mayreadily be made of such frequency characteristics 'that it will respondto these low frequency-signals but will serve as a choke to the normalhigher frequencies.. Alternatively a second means of utilizing thesignalling characteristics of the device is to allow-the audio output ofdemodulator .3l rather than the direct pulses to energize relay 29.Under this condition an audio tone corresponding to the divided pulsefrequency will be obtained at the output of the demodulator and Vwhichis of suiiiciently low frequency to be passed by filter 28 and excitethe buzzer 29. For this type of operation, connection is made to thebuzzer 29, from the output side of demodulator 3 I.

It is thus clear in our invention that we have provided a very simpleform of signaling system. It is only necessaryto operate switch I1 to aposition including in series frequency divider I6 in order to signal todemodulator 2|. When the signaling is not taking place, switch I'I isreturned to a position to directly connect modulator II to line I8withoutthe frequency divider Iii in series.

In order similarly to signal from modulators I2 and I3 we providefrequency dividers IBA and IEB connectable into the line by means ofswitches-IIA, IIB, respectively. The signaling frequencies produced byfrequency dividers IBA and ISB are selected in demodulators 22 and 23,respectively, and applied to the respective outputs at 28A, 29A andr28B,29B t-o signal these other selected stations. y It should be noted thata single frequency divider may be used for all channels in place of theindividual dividers by providing the proper switching arrangement.

It is clear vthat any desired form of frequency divider may be used inplace of the type diagrammatically illustrated. Furthermore, other formsof signaling equipment than the simple buzzers may be provided. ifdesired, at the receiving end.

While we have described above the principles of our invention inconnection with specific apparatus, and particular modificationsthereof, it is to be clearly understood that this description is madeonly by way of example and not as a limitationon the scope of ourinvention as set forth in the objects of our invention and theaccompanying claims.

What is claimed is: f

1. In a transmission system of the type wherein intelligence istransmitted by modulation of a train of impulses repeated at a cadenceabove the highest frequency of said intelligence, a system of signalingcomprising means for effectively selecting certain discrete impulses ofsaid .train at regularly recurring intervals, whereby telligencenormally transmitted thereby, a transmission "medium for said impulses,receiver means for receiving said'impulses after transmis- -sion oversaid medium, a frequency divider for reducing said cadence frequency toalower signal frequency cadence,A means for selectively inserting saidfrequency divider between said impulse source and said medium, and meansin the .output of said receiver means responsive to said signal cadencefrequency impulses to produce a signal indication at said receiver.l 1 YY 3. In a communication system of -the Atype wherein intelligence istransmitted from a transmitter through a transmission medium in the formof a train of modulated impulses repeated at a cadence above the highestfrequency of -said intelligence to a receiver; a signaling arrangementcomprising a selector for selecting discrete impulses of said train atregularly recurring intervals whereby there is provided at the output ofsaid selector a train of impulses recurring at a cadence equal to theperiodV of a lower frequency, means for selectively coupling saidtransmitter either directly to said transmission medium or through saidselector to said medium, and signal means at said receiver responsive tosaid impulses of said lower frequency coupled to said receiver forproducing said signals.

4. A transmission system comprising a source of impulses for producingimpulses having ancrmal spacing providing a cadence frequency for saidimpulses higher than the frequency of Vintelligence normally transmittedthereby, a transmission line for said impulses, receiver means forreceiving said impulses after transmission over` said line, a frequencydivider for reducing said cadence frequency to a lower signal frequencycadence, means for selectively inserting said frequency divider intosaid line, and means in the output oi said receiver means responsive tosaid signal cadence frequency impulses to produce a signal indication atsaid receiver.

5. In a multi-channel communication system wherein communication iscarried on between a plurality of transmitters and a correspondingplurality of receivers over a common transmission medium, each of saidtransmitters providing a train of impulses spaced apart by a regulartime interval to produce a cadence frequency above the highest frequencyat which intelligence is normally to be transmitted, and each of saidreceivers serving to receive and demodulate the corresponding train ofimpulses from the transmitters and apply it to an individual outputline, a system for selectively signaling from any one of saidtransmitters to the corresponding receiver comprising a frequencydivider means for each said transmitter to provide for reduction of said5 cadence frequency to a signal frequency, means for selectivelyconnecting each frequency divider in the output of its correspondingtransmitter, and signal responsive means tuned to respond to said signalfrequency, coupled to the output 5 .transmission line at each receiver.

6. A multi-channel communication system according to claim 5 furthercomprising a synchronizing wave source at the transmitter terminal anda, second synchronizing source at the receiver 10 terminal for normallysynchronizing the operation of said transmitters and said receivers, andmeans coupling said synchronizing source at said transmitter terminal inphase controlled relation to said frequency dividers to synchronize 15REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS Number Name Date '2,204,375 Morrison June 11, 19402,213,941 Peterson Sept. 3, 1940 2,326,584 Van Zeist 1 Aug. 10, 19432,048,081 Riggs July 21, 1936 2,172,354 Blurnlein Sept. 12, 19391,484,405 Oswald Feb. 19, 1924 1,532,336 Nottage et al. Apr. '7, 19252,263,369 Skillman Nov. 18, 1941 FOREIGN PATENTS Number Country Date418,525 Great Britain Oct. 26, 1934

